1. Field of the Invention
The present invention relates to a semiconductor device having an SOI (silicon on insulator) structure and a method for manufacturing the semiconductor device. In this specification, the semiconductor device refers to any device which can function with the use of semiconductor characteristics.
2. Description of the Related Art
In recent years, LSI technology has been dramatically progressed, and an SOI structure by which speeding up and low power consumption are realized has been attracted attention. In this technology, an active region (channel formation region) of a field-effect transistor (FET), which has been conventionally formed using bulk single crystal silicon, is formed using a single crystal silicon thin film. It is known that a MOS field-effect transistor manufactured using an SOI structure has lower parasitic capacitance than that manufactured using a conventional bulk single crystal silicon substrate, and such a MOS field-effect transistor is advantageous for speeding up.
Examples of substrates having SOI structures (hereinafter, also referred to as SOI substrates) include SIMOX substrates, bonded substrates, and the like. For example, for an SOI structure of a SIMOX substrate, oxygen ions are implanted into a single crystal silicon substrate, and heat treatment at 1300° C. or higher is conducted to form a buried oxide film (BOX) layer, so that a single crystal silicon thin film is formed on the surface. In the SIMOX substrate, a single crystal silicon thin film having an even thickness can be formed with high control by precise control of oxygen ion implantation; however, there is a problem in that long time period is needed for oxygen ion implantation, thereby causing problems of time and costs. Further, there is another problem in that the single crystal silicon thin film is easily damaged in the oxygen ion implantation.
For a bonded substrate, an SOI structure is obtained in such a manner that two single crystal silicon substrates (a base substrate and a bond substrate) are bonded to each other with an oxide film interposed therebetween, and one of the single crystal silicon substrates (the bond substrate) is thinned by grinding and/or polishing on its rear side (the side which is not a surface to be bonded), so that a single crystal silicon thin film is formed. Since it is difficult to form a uniform, thin single crystal silicon thin film by grinding and/or polishing, there is proposed a technique for thinning a film which employs hydrogen ion implantation, which is so-called Smart-Cut (registered trademark) (e.g., Reference 1: Japanese Published Patent Application No. H5-211128).